The present invention relates generally to an axial lead frame. More particularly, the present invention relates to a contour to be assumed by an axial lead frame which is used for the purpose of producing electronic components each having two poles located opposite to each other, e.g., diode devices, light emitting diode devices or the like.
A contour assumed by a conventional axial lead frame (hereinafter referred to simply as a lead frame) of the foregoing type will be described below with reference to FIG. 3 with respect to a lead frame to be used for producing diode devices.
The lead frame designated by reference numeral 1 includes two side rails 3 and 4 located opposite to each other, and a plurality of joint pieces 2 arranged in the equally spaced relationship in the longitudinal direction are bridged between both the side rails 3 and 4. In addition, a predetermined number of lead terminals 5 and 6 (each six terminals in the shown case) separated from each other and located opposite to each other are arranged in the equally spaced relationship to extend in parallel with each other in each segment defined by adjacent joint pieces 2. A die pad 7 is formed at the foremost end of each lead terminal 5 for the purpose of die-bonding a diode element thereto, while a pad 8 is formed at the foremost end of each lead terminal 6 for the purpose of connecting thereto one end of a fine metallic lead wire connected to the corresponding diode element. Generally, the lead frame 1 contoured in the aforementioned manner is produced by employing a punching process using a punching die.
Next, a procedure of producing a diode device using the lead frame 1 will be described below.
First, a diode element is die-bonded to each die pad 7, and subsequently, the diode element die-bonded in that way is connected to the corresponding pad 8 via a fine metallic lead wire. On completion of the connecting operation, an assembly consisting of one segment of the lead frame 1, diode elements die-bonded to pads 8 and fine metallic lead wires is subjected to molding as illustrated by phantom lines R in FIG. 3. To test electrical properties of each diode device produced in that way, one of the lead terminals 5 or 6 is cut off from the side rail 3 or 4. Testing is executed with the diode device by connecting a common measuring pin to the side rail 3 or 4 which holds lead terminals 5 or 6 without any connection to the diode device and then connecting another measuring pin to the lead 5 or 6 which is cut off therefrom. On completion of the testing, the lead terminal 5 or 6 which is not connected to the diode device which has been confirmed as an acceptable one is cut off from the side rail 3 or 4.
With resect to the conventional lead frame constructed in the above-described manner, however, the following problems have been arisen.
With the conventional lead frame 1, a plurality of joint pieces 2 should be arranged in the equally spaced relationship in the longitudinal direction for connecting the side rails 3 and 4 to each other which hold plural pairs of lead terminals 5 and 6 separated from each other. For this reason, the number of diode devices obtainable per a unit length of the lead frame 1 is unavoidably restricted. Thus, there arises a problem that each diode device is produced not only at an expensive material cost but also at an expensive production cost. When each joint piece 2 is designed to have a smaller width or a pitch between adjacent joint pieces 2 is elongated in order to increase the number of diode devices obtainable per a unit length of the lead frame 1, there arises another problem that the joint strength of the lead frame 1 is undesirably reduced.
As mentioned above, the lead frame 1 is generally produced by employing a punching process using a punching die, and the punching die includes punches each adapted to repeatedly punch a pattern enclosed by the phantom lines R (consisting of a single joint piece 2 and plural pairs of lead terminals 5 and 6 arranged in the equally spaced relationship to extend in parallel with each other in the space defined between adjacent joint pieces 2) as shown in FIG. 3. Thus, each lead frame 1 having a plurality of patterns each having a same contour successively arranged in the longitudinal direction is produced by simultaneously punching them from a metallic sheet material in the punching die. Due to the fact that the conventional lead frame 1 includes a plurality of joint pieces 2 arranged in the equally spaced relationship in the longitudinal direction, a pitch between adjacent joint pieces 2 is elongated, and moreover, the number of punches required for the punching die increases correspondingly. Thus, there arises another problem that the punching die becomes complicated in structure, resulting in it being produced at an expensive cost.